Material adverse change (MAC)

Definition

A clause letting a buyer walk if the business is badly damaged.

Why It Matters

It is the buyer's escape hatch when the business or the world turns badly between signing the purchase agreement and closing. How broadly it is drafted decides whether a lost key customer or a soft quarter actually lets you walk or renegotiate, so it is one of the clauses most worth lawyering rather than accepting as boilerplate.

In numbers: Between LOI and close, a customer worth 30% of revenue gives notice; the MAC clause is what lets the buyer walk or reprice instead of closing on a business that no longer exists as priced.